The present invention relates to a method and apparatus for transmitting and receiving information across a wireless link using a plurality of antennas. More particularly, the present invention relates to a method and apparatus for selecting an optimal set of antennas from a plurality of antennas for use by a transmitter and/or receiver for improving any performance criterion (such as data rate, error rate, etc) over a wireless link.
Current wireless systems generally use single antennas at the transmitter and receiver. For a broad class of wireless systems including mobile and satellite communications, personal communication and wireless network systems, system performance, such as data rate, error rate, etc., can be improved substantially by the use of multiple antennas at the transmitter and/or the receiver.
Different approaches and concerns in implementing such multiple antenna systems are, for example, described in “On Limits of Wireless Communications in a Fading Environment When Using Multiple Antennas” by G. J. Foschini et al, Wireless Personal Communications, Kluwer Academic Publishers, vol. 6, No. 3, pages 311-335, March 1998 (Reference 1); “Capacity of Multi-Antenna Array Systems In Indoor Wireless Environment” by C. Chuah et al, Proceedings of Globecom '98 Sydney, Australia, IEEE 1998, pages 1894-1899 November 1998 (Reference 2); “Fading Correlation and Its Effect on the Capacity of Multi-Element Antenna Systems” by D. Shiu et al, IEEE Transactions on Communications vol. 48, No. 3, pages 502-513 March 2000 (Reference 3); “The Impact of Antenna Diversity On the Capacity of Wireless Communication Systems”, by J. H. Winters et al, IEEE Transactions on Communications, vol. 42, No. 2/3/4, pages 1740-1751, February 1994 (Reference 4); “Capacity of Multi-Antenna Gaussian Channels” by E. Telatar, AT&T-Bell Labs. Internal Technical Memorandum, June 1995 (Reference 5); “Increasing capacity in wireless broadcast systems using distributed transmission/directional reception (DTDR)” U.S. Pat. No. 5,345,599.
From the references cited above, it is clear that multiple antennas at the transmitter and/or receiver can be used to increase data rate through spatial multiplexing or reducing error-rate through diversity (space-time/space-frequency coding) or beam-forming. Future configurations may move towards striking a balance between these techniques. Deployment of multiple antenna technology requires the development of advanced space-time/space-frequency processing at the transmitter and receiver. Our invention while facilitating the use of multiple-antenna technology is not restricted to any particular space-time/space-frequency processing at the transmitter and/or receiver but is generally applicable to any wireless transmission/reception scheme employing a plurality of antennas at the transmitter and/or receiver. The particular transmission/reception scheme used will impact the implementation of this invention and vice versa.
Although increasing the number of antennas for transmitting and/or receiving in a wireless system improves the performance of a wireless link, there are some limitations on the applicability of such a strategy. Namely, in such systems for every transmit antenna and every receive antenna a separate RF chain must be provided. Thus, as the number of antennas at transmitter or receiver increase so do the number of RF chains required.
RF (Radio-frequency) chains (transmitter RF chains in particular) are much more expensive than the antenna elements. Thus, increasing the number of antennas in such systems would in effect increase the cost of the system.
Therefore, there is a need to provide a technique that takes advantage of the benefits provided by the use of a multiple antenna configuration without unnecessarily increasing the cost of the apparatus. In addition, under certain circumstances, system performance can be improved by using fewer RF chains than antennas available. The key idea of this patent, namely selection of an optimal set of antennas from a plurality of available antennas at the transmitter and/or receiver to connect the RF chains to is equally applicable in both cases.
Existing patents in related areas include “Receive antenna selection method and diversity receiver”, U.S. Pat. No. 6,141,392, “Impairment determination for a diversity antenna selection process”, U.S. Pat. No. 6,118,773, “Diversity antenna selection”, U.S. Pat. No. 6,002,672 and “Method and arrangement for antenna selection control in a radio receiver”, U.S. Pat. No. 5,991,613. All of the above patents are concerned with only single antenna selection at either the transmitter or receiver. None of them refer to multiple antenna selection and are concerned mostly with improving diversity in the system. Our invention deals with the selection of multiple sets of antennas at the transmitter and/or receiver for any criterion such as spatial multiplexing, beam-forming, diversity etc. Our invention is novel and sufficiently different from those mentioned above.